Gems are socketable items in Torchlight. Most are some form of Ember. Socketed equipment allow players to add gems to them, which give additional bonuses such as increased health or resistances.
Gems may be upgraded by Duran the Transmuter, who can combine two gems of the same type and quality into a gem of the next higher level of quality.
The only exception to this are chaos gems, which cannot be transmuted. Below are tables listing all the types of socketable gems.